The influence of self-excited forces on wind loads and wind effects for super-large cooling towers

The self-excited force induced by the interaction between the structure and airflow has been technically ignored in previous studies conducted on wind loads and wind effects for super-large cooling towers. Moreover, no criteria could be used for qualitative and quantitative studies of the effects resulting from the self-excited force. In this study, by taking a Chinese super-large cooling tower for nuclear power with a height of 215 m as an example, the wind tunnel test of cooling tower aero-elastic model with simultaneous pressure and vibration measurement through a modified equivalent beam-net design method was firstly carried out, in which external wind loads of super-large cooling towers were obtained with the presence of the self-excited force. Firstly, the effects of self-excited force on distribution characteristics of external mean and fluctuating wind pressures were analyzed. Through the refined frequency-domain algorithm of wind-induced responses from our previous studies, wind-induced responses of super-large cooling towers were calculated by considering two cases of wind tunnel tests with or without self-excited force. Subsequently, the effects of self-excited force on wind-induced responses and Gust Response factors of super-large cooling towers were discussed. The results showed that the self-excited force had weak influence on the distribution of external mean wind pressure of the super-large cooling tower, while it significantly affected distribution and values of fluctuating wind pressure. Moreover, the effects of self-excited force on wind-induced mean response were negligible for the super-large cooling tower. The response differences calculated using two aerodynamic parameters were mostly below 5%, and regardless of whether or not to consider the influence induced by self-excited force. The excitation mode of wind-induced resonant response was consistent even at the maximum error (i.e. 10%). Furthermore, this study indicated that the influence of self-excited force on wind effects was advantageous to majority of regional structures. To overcome the problems existing in aero-elastic model, e.g., accuracy, accessibility and cost of test, this study suggested that external wind load model without self-excited forces obtained by pressure test of rigid body could be used to calculate the wind-induced responses of super-large cooling towers, in which the differences were within an acceptable range.